This disclosure refers to beehives wintered outdoors.
To sustain life and produce warmth during winter, the bees consume honey. The main by-products of honey assimilation by the bees are carbn dioxide and water. For each pound of honey consumed, about 0.66 pounds of water and about 1.22 pounds of carbon dioxide are produced. When the outdoor temperature falls below about 44 degrees F., the bees form a cluster in the hive to conserve heat. During winter, the bees do not control the temperature within the hive outside the cluster. Indeed, the temperature outside the cluster is only a few degrees above the ambient outside air temperature. Under such conditions the water vapour, formed by assimilation of honey, which was not ventilated out, will condense and sometimes freeze on the cold internal surfaces of the beehive and frames with comb.
The aforementioned carbon dioxide, however, must be ventilated out in order that fresh air can enter the beehive. Without adequate supply of oxygen the bees can not assimilate the honey, and they will suffocate.
Starting about the middle of summer, the bees propolise all small cracks, which would allow air passage to the outside. However, cracks exceeding about 3/16" height can not be successfully propolised because the propolis is soft and therefore flows during hot summer weather. Deteriorating equipment, like rolled out corners of the brood chambers, are likely to have larger holes which can not be propolised. The bees are able to winterise their hive by propolising only during warm weather, when the propolis is soft. If the inner cover was opened up, for whatever reason, late in fall, the bees will not be able to again propolise the interface between the inner cover and the upper brood chamber because it is too cold.
A beehive prepared for wintering by a beekeeper normally has a reduced, but open, front bottom bee entrance. If any cracks or openings do exist on either of the side walls, back wall, or in the inner cover, except for the openings on the front wall, the beehive will be subjected to a draft of air blowing through the hive during windy periods.
Overventilation caused by a draft through the hive can also freeze the bees. For continuous survival, the bees on the outer layer of the cluster maintain the minimum temperature of about 44 degrees F. irrespective of the outside temperature. A draft through the hive during a cold spell may remove more heat from the hive than the cluster can produce. As a result, the outer layer of bees on a cluster will freeze and drop off, exposing the next layer of bees to the same condition, until the entire cluster of bees dies out.
In the fall when the outdoor temperature drops below 44 degrees F., the bees in the hive form a cluster, generally in the lower brood chamber. As they consume honey they move upward, and in two to three months the cluster will reach and contact the inner cover of the upper brood chamber. During all this and the subsequent period, the bees must have continuous ventilation to provide an adequate oxygen supply in order to survive.